Fig. 3. The effects on ventilation rate (percentage change from starting values) of graded hypoxia, hyperoxic hypercarbia, hyperoxia and injections of NaCN externally into the respiratory water. The data are shown as the mean + S.E.M. (N=8-12). In each graph, the different groups are C, control; GD, gills denervated; GOD, gills and orobranchial cavity denervated; DC, decerebrate control; DGD, decerebrate, gills denervated; DGOD, decerebrate, gills and orobranchial cavity denervated. Asterisks indicate values that are significantly different from resting values for fish within that group under normoxic normocapnic conditions (100 % value).